Semiconductor die assemblies, semiconductor devices including same, and methods of fabrication

ABSTRACT

Methods of fabricating multi-die assemblies including a wafer segment having no integrated circuitry thereon and having a plurality of vertically stacked dice thereon electrically interconnected by conductive through vias, resulting multi-die assemblies, and semiconductor devices comprising such multi-die assemblies. The wafer segment may function as a heat sink to enhance heat transfer from the stacked dice in the resulting multi-die assembly. The die stacks are fabricated at the wafer level on a base wafer, from which the wafer segment and die stacks are singulated after at least peripheral encapsulation.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.13/192,014, filed Jul. 27, 2011, which issued on Oct. 8, 2013, as U.S.Pat. No. 8,552,567, the disclosure of which is hereby incorporatedherein in its entirety by this reference.

TECHNICAL FIELD

Embodiments of the present disclosure relate to semiconductor dieassemblies, to semiconductor devices including such assemblies, and tomethods of fabrication of the assemblies.

BACKGROUND

Increased circuit density is an ongoing goal of manufacturers ofsemiconductor devices. One long-favored configuration is an assembly ofvertically stacked semiconductor dice, at least some of which areinterconnected electrically and the stacked die assembly beingmechanically and electrically connected to higher level packaging, suchas an interposer or other substrate bearing conductive traces.

One configuration employing a plurality of stacked semiconductor dice isa Micropillar Grid Array Package (“MPGA”). Such a package comprises astack of a plurality (for example four (4)) of dynamic random access(DRAM) semiconductor memory dice vertically interconnected from anuppermost die to a lowermost die, and a plurality of conductive pillarsextending from the underside of the lowermost memory die for connectionto a logic die or a System on a Chip (SoC) die.

The provider of the logic die or the SoC die conventionally mounts theirdevice to an interposer, such as a ball grid array (BGA) substrate, thelogic or SoC die including conductive through vias for connection to theconductive pillars on the underside of the MPGA. The MPGA is mounted tothe logic die or SoC die on the interposer, and the assembly is thenovermolded with an encapsulant into a finished BGA package.

The aforementioned configuration, implemented as a so-called “Wide I/O”memory device, enables fast memory access, and reduces powerrequirements.

The end product finds application, among others, in mobile electronicdevices such as so-called “smart phones” exemplified by BLACKBERRY®devices, iPHONE® devices, and DROID® devices, among others.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A through 1K illustrate an embodiment of a method for forming asemiconductor structure according to the present disclosure;

FIGS. 2A through 2M illustrate another embodiment of a method forforming a semiconductor structure according to the present disclosure;

FIGS. 2N and 2O depict, respectively, a side sectional elevation and anend (bottom) elevation of a completed, stacked die package formed by themethod of FIGS. 2A through 2L;

FIGS. 3A through 3C schematically illustrate a sequence for fabricationof a semiconductor device including a stacked die structure according toembodiments of the present disclosure, and the resulting semiconductordevice;

FIG. 4 is a plan view of a portion of the base wafer depicted in FIG.1A;

FIG. 5 is a plan view of a portion of the base wafer of FIG. 2G showingrecesses RE as depicted in broken lines at the left-hand side of FIG.2G; and

FIG. 6 is a plan view of another portion of the base wafer of FIG. 2Gshowing recess RD as depicted in broken lines at the right-hand side ofFIG. 2G.

DETAILED DESCRIPTION

Semiconductor die assemblies are disclosed, semiconductor devicesincluding same, and methods of fabricating same. As used herein, theterm “wafer” means and includes a volume of a semiconductor material inthe form of a bulk semiconductor substrate, and is not limited toconventional, substantially circular wafers. As used herein, the term“semiconductor material” means and includes silicon, germanium, galliumarsenide, indium phosphide, and other III-V or II-VI type semiconductormaterials. As used herein, the terms “semiconductor die” and “die” andplural forms thereof, means and includes a segment or segments bearingintegrated circuitry and singulated from a bulk semiconductor substrate.As used herein, the term “memory die” and plural forms thereof means andincludes all forms of integrated circuit memory, by way of non-limitingexample including DRAM, SRAM, Flash memory, and other memory forms.While only a few semiconductor dice and associated wafer segments aredepicted in the drawing figures for clarity, it is of courseconventional that hundreds or even thousands of dice may be fabricatedon, and singulated from, a single source wafer. Likewise, hundreds oreven thousands of segments may be singulated from a single base wafer.

The following description provides specific details, such as materialtypes and processing conditions in order to provide a thoroughdescription of embodiments of the present disclosure. However, a personof ordinary skill in the art will understand that the embodiments of thepresent disclosure may be practiced without employing these specificdetails. Indeed, the embodiments of the present disclosure may bepracticed in conjunction with conventional semiconductor fabricationtechniques employed in the industry. In addition, the descriptionprovided below does not a complete process flow for manufacturing asemiconductor device. Only those process acts and structures necessaryto understand the embodiments of the present disclosure are described indetail below. Additional acts to form a complete semiconductor devicefrom the semiconductor structures may be performed by conventionalfabrication techniques.

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof, and in which is shown,by way of illustration, specific embodiments in which the presentdisclosure may be practiced. These embodiments are described insufficient detail to enable a person of ordinary skill in the art toimplement embodiments of the present disclosure. However, otherembodiments may be implemented, and structural, logical, and electricalchanges encompassed by the disclosure may be made. The illustrationspresented herein are not meant to be actual views of any particularassembly, memory device, logic device, or system, but are merelyidealized representations that are employed to more completely describethe embodiments of the present disclosure. The drawings presented hereinare not necessarily drawn to scale. Additionally, elements commonbetween drawings may retain the same or a similar numerical designation.

Employing a fabrication process according to some embodiments of thepresent disclosure offers significant advantages to both the manufactureand resulting product in the form of stacked die assemblies, includingwithout limitation, MPGA packages. For example, the singulation of abase wafer with a plurality of spaced semiconductor die stacks thereonbetween the die stacks enhances thermal performance of each resultingdie stack package by providing a heat sink in the form of the singulatedbase wafer segment. Use of a relatively thick, robust base wafer tofabricate stacked die packages thereon enhances mechanical strength andfacilitates handling of the assembly, while thinning of the base waferprior to singulation enables reduction of the height of the resultingstacked die package. The base wafer segment, which does not includeactive circuitry, may be laser marked without fear of damage to anultra-thin active die. An encapsulation structure formed around each diestack provides mechanical protection for relatively fragile, thinsemiconductor dice incorporating conductive through vias. Thedie-to-wafer process employed for stacking results in the ability to usewafer level processes downstream, enabling higher throughput and reducedcosts. For example, wafer level testing of the encapsulated die stacksmay be performed before singulation. In addition, the use of a basewafer allows for a larger step size, due to the larger die pitch enabledby the use of the spaced die stacks on the base wafer during wafer levelpackaging, so that a standard scribe width may be employed. Further, theuse of known good die (KGD) minimizes packaging costs.

One embodiment comprises a method of forming a semiconductor dieassembly, comprising securing a plurality of laterally spacedsemiconductor dice having conductive through vias to a base wafer havingthermally conductive elements protruding therefrom in alignment with theconductive through vias, stacking a plurality of semiconductor die overeach semiconductor die of the plurality of laterally spacedsemiconductor dice and connecting conductive through vias of stackedsemiconductor dice with conductive elements extending therebetween. Adielectric material is introduced between the semiconductor dice and atleast a periphery of the semiconductor dice on the base wafer areencapsulated with an encapsulant material between and around thesemiconductor dice, followed by severing through the encapsulantmaterial and through the base wafer between stacks of semiconductordice.

Referring now to FIGS. 1A through 1G of the drawings, a process sequencefor fabrication of a semiconductor die stack according to an embodimentof the present disclosure is described.

FIG. 1A depicts a side sectional elevation of a base wafer 100 b ofsemiconductor material, for example silicon, of a thickness of about 500μm to about 800 μm. FIG. 4 depicts a plan view of a portion of basewafer 100 b showing several die stack locations DS thereon in brokenlines, with streets S therebetween, the width of streets S beingexaggerated for clarity. In one embodiment, base wafer 100 b has nointegrated circuitry fabricated thereon. A dielectric material 104 inthe form of a film or other coating is applied over surface 102,followed by fabrication or application of a plurality of thermallyconductive elements 106, which may also be electrically conductive andwhich are electrically isolated from base wafer 100 b by dielectricmaterial 104 and which are laterally spaced and, thus, mutuallyelectrically isolated as depicted in FIG. 1A and FIG. 4. Thermallyconductive elements may comprise metal pillars, which may also becharacterized as columns or studs, or solder balls. If metal pillars areemployed, copper, as one suitable material, may be electroplated on aseed layer (not shown) on dielectric material 104, or sputtered ontodielectric material 104, as is conventional. Thermally conductiveelements 106 may then be formed by masking, patterning of the mask, andremoval of the unmasked thermally conductive material by a conventionaltechnique, such as etching, to form electrically isolated pillars. Othermetals and alloys, for example gold and silver, may be employed. Anotherapproach for pillar formation is application of a seed layer, masking ofthe seed layer, and forming pillars by electroplating on unmaskedportions of the seed layer providing pillar locations, followed byoptional removal of the mask and unplated seed layer. If solder ballsare employed, segments of a solder paste may be applied to isolatedmetallic pads formed or otherwise disposed on dielectric material 104and reflowed to form solder balls, or preformed solder balls may beapplied to the pads and reflowed sufficiently to bond thereto. By way ofexample only, thermally conductive elements 106 in the form of 20 μmdiameter copper pillars may be employed, at a 40 μm minimum pitch.

FIG. 1B depicts a schematic cross-section of an active device in theform of semiconductor memory die 110, which has been prepared forstacking. Memory die 110 comprises integrated circuitry 112 on an activesurface 114 thereof, on which a plurality of thermally and electricallyconductive elements 116 are formed over conductive through vias 118,which may also be referred to for the sake of convenience using theindustry term “through silicon vias,” or “TSVs,” and which extend to aback side 120 of memory die 110. TSVs 118 terminate on back side 120 atconductive landing pads 122 or at traces of a redistribution layer (RDL)extending to landing pads 122. The landing pads 122 are located to alignwith thermally conductive elements 106 of base wafer 100 b , withthermally and electrically conductive elements 116 of another memory die110 or with connective elements of a logic die or a SoC die, as will besubsequently described. Conductive through vias 118 may be formed usingconventional techniques, as may be the RDL, if employed, and landingpads 122.

For example, the enlarged view of FIG. 1C shows through via precursorstructures 118′ formed in a desired pattern partially through a sourcewafer 100 s using wafer level processing after fabrication of integratedcircuitry 112 on active surface 114 at each location for a memory die110 by etching, then lined with a dielectric, and lined or filled with aconductive material. Subsequently, thermally and electrically conductiveelements 116 may be formed as depicted in FIG. 1D, as described abovewith reference to formation of thermally conductive elements 106 of FIG.1A. As also shown in FIG. 1D, the source wafer 100 s may then be thinnedT as indicated by broken line to expose the via ends and form conductivethrough vias 118, resulting in a die of about 50 μm thickness, by way ofnon-limiting example. The RDL, if employed, and landing pads 122 (FIG.1E), may then be faulted. Memory die 110 is a so-called known good die,abbreviated as KGD, meaning memory die 110 has been tested to specificperformance parameters for the intended application for the die 110.

More specifically, source wafer 100 s has a passivation material 115,such as a polyimide, polybenzoxazole (PBO), or bismaleimide Triazine(BT) resin, or silicon nitride or a silicon oxide, applied to activesurface 114, and thermally and electrically conductive elements 116comprising metal pillars, such as copper pillars, may be formedthereover. Other metals and alloys, for example of gold and silver, maybe employed. Thermally and electrically conductive elements 116 may alsocomprise solder balls, which may be formed as described above byreflowing solder paste segments or partially reflowing preformed solderballs on under bump metallization (UBM), for example nickel, exposedthrough apertures in a silicon nitride passivation layer.

Source wafer 100 s with thermally and electrically conductive elements116 formed thereon may be mounted on a temporary carrier TC (FIG. 1E) asknown in the art and thinned to, for example, a thickness of about 50 μmto expose the ends of conductive through via precursor structures 118′on the back side 120 of each base wafer 100 b, forming conductivethrough vias 118. An abrasive process, such as back grinding, followedby a fluorine or chlorine-based reactive ion etching (RIE) silicon dryetch process, may be used to thin source wafer 100 s.

The back side 120 of thinned source wafer 100 s′ is coated with apolymer passivation material 121, such as a polyimide, PBO or BT resin,or silicon nitride or a silicon oxide, and solderable interconnects inthe form of landing pads 122, for example, of nickel on the ends ofconductive through vias 118 comprising copper, are formed byelectroplating over passivation material 121 and in contact withconductive through vias 118 through openings in passivation material121, then masking and etching to define landing pads 122.

Thinned source wafer 100 s′ is mounted to a film frame, and thetemporary carrier is removed. Thinned source wafer 100 s′ is thensingulated into individual dice 110.

As depicted in FIG. 1F, a plurality of laterally spaced memory dice 110a having conductive elements 116 extending from surfaces thereof areremoved from a thinned source wafer 100 s′ after singulation therefromusing a conventional pick and place operation and placed on, and bondedto, base wafer 100 b at die stack locations DS by landing pads 122 onback sides 120 thereof aligned with thermally conductive elements 106.

As depicted in FIG. 1G, additional memory dice 110 b, 110 c and 110 dhaving conductive elements extending from surfaces thereof may berespectively stacked and secured, one above the other, onto and orientedin a common direction (for example, active surface 114 facing away frombase wafer 100 b) as each memory die 110 a secured to base wafer 100 b.It is also contemplated that memory dice 100 a through 110 d may bemixed in orientation, with thermally and electrically conductiveelements 116 and landing pads 122 formed over either an active surface114 or a back side 120 of a given die 110, as desired to facilitatestacking thereof. Further, and as described below with regard to anotherembodiment of the disclosure, dice of a given die stack may be orientedwith active surfaces facing a base wafer. The semiconductor dice 110 athrough 110 d of each die stack may be electrically and mechanicallyconnected, and secured to base wafer 100 b, using conductive elements106 and 116 one level at a time, or after all the die stacks arecompleted.

As noted, stacking additional memory dice comprises stacking at leasttwo semiconductor dice over each semiconductor die of the plurality oflaterally spaced semiconductor dice secured to the base wafer and mayfurther comprise stacking at least two semiconductor dice havingconductive elements extending from surfaces thereof.

All memory dice 110 a through 110 d employed to repopulate base wafer100 b have been qualified as KGD. As illustrated, each completed diestack 130 comprises four memory dice 110 a-110 d, but the disclosure isnot so limited.

After placement of each level of dice 110 a through 110 d on base wafer100 b, thermally conductive elements 106 and thermally and electricallyconductive elements 116 may be bonded to landing pads 122 at the waferlevel using a conventional thermocompression or ultrasonic bondingprocess one level at time, if metal pillars are employed, or a reflowoperation, if solder bumps are employed or a solder material isdisposed, for example, between elements 116 comprising copper pillarsand landing pads 122.

As depicted in FIG. 1H, a dielectric material in the form of capillaryunderfill 132 is applied and cured between base wafer 100 b and memorydice 110 a through 110 d of each die stack 130 about thermallyconductive elements 106 and thermally and electrically conductiveelements 116. If desired, an epoxy underfill material 132′ may bepre-applied to memory dice 110 a through 110 d in lieu of the use of acapillary underfill, and cured.

Referring to FIG. 1I, base wafer 100 b, populated with die stacks 130,is then subjected to a wafer level molding process to provide anelectrically insulative, which may also be characterized as adielectric, encapsulation structure 134 around and between the diestacks 130 including memory dice 110 a-110 d for mechanical andenvironmental protection thereof and in contact with base wafer 100 b,forming a plurality of unsingulated, encapsulated die stacks 136 on basewafer 100 b . One particularly suitable technique is film assistmolding, as described in U.S. Pat. Nos. 7,595,017; 6,652,799; and6,459,159, which process protects the integrity of thermally andelectrically conductive elements 116 protruding from memory dice 110 d.

After molding of the encapsulation structure 134 and as indicated inFIG. 1J, base wafer 100 b is back ground to thin it from its initial 500μm to 800 μm thickness to, for example, about 100 μm to about 150 μm,resulting in thinned base wafer 100 b′.

After thinning of base wafer 100 b, a test of each die stack 130 isconducted, and good die stack locations determined by a test are marked.

After encapsulation, and as depicted in FIG. 1K, thinned base wafer 100b′ and encapsulation structure 134 thereover is singulated between diestacks 130 and through thinned base wafer 100 b′ along street S (FIG. 4)to form a plurality of stacked die packages 140 each including a wafersegment 138, which may also be characterized as a support and heat sinksegment, and memory dice 110 a through 110 d, the wafer segment 138being of greater lateral extent than the semiconductor dice 100 athrough 110 d. Stacked die packages may, as depicted in FIG. 2M withrespect to a subsequent embodiment, be placed in pockets in a tape forshipment to and use by a customer.

In the foregoing embodiment, the die stack 130 may comprise functionallydifferent semiconductor dice in addition to, or in lieu of, memory dice.In other words, the architecture of die stack 130 and stacked diepackage 140 is adaptable to applications other than memory die stacks,and specifically MPGA packages as mentioned above. For example,semiconductor die 110 a may comprise a logic die.

In another embodiment of the disclosure, it is contemplated that basewafer 100 b and resulting base wafer segment 138 may incorporateintegrated circuitry and be operably coupled using thermally conductiveelements 106, which in such an instance would also be formed of anelectrical conductive material and correspond to thermally andelectrically conductive elements 116 in function, and due to the absenceof dielectric material 104, to the remainder of the semiconductor dicein die stack 130. One application for such a configuration is tofabricate base wafer 100 b with integrated circuitry 112 as shown inbroken lines in FIG. 1A and to only employ three other memory dice 110a-110 c, to provide a stack of four memory dice while maintainingpackage height within required parameters to enable use of a larger(thicker) logic or SoC device at the base of the die stack.

A further embodiment comprises a method of forming a semiconductor dieassembly, comprising securing a plurality of laterally spacedsemiconductor dice to a base wafer, disposing at least two semiconductordice over each semiconductor die of the plurality to form a stack andconnecting conductive through vias of the semiconductor dice in a stackwith conductive elements extending therebetween. A dielectric materialis provided between the semiconductor dice in a stack, and at least aperiphery of each of the stacks of semiconductor dice on the base waferis substantially simultaneously encapsulated with an encapsulantmaterial between and around the stacks of semiconductor dice and thestacks of semiconductor dice and the base wafer are singulated throughthe encapsulant material between the stacks of semiconductor dice.

In this embodiment, a process flow for fabrication of which is depictedin FIGS. 2A through 2M, stacked dice with conductive through vias aremounted to a base wafer segment oriented in a common, face-downdirection, wherein the active surfaces of the dice face the base wafersegment and, consequently, are protected during processing or handlingof the die stack. As such an orientation results in probe and/or testpads being inaccessible for testing of the stacked die package, backside contacts on the most distant die from the base wafer are providedfor testing, in addition to interconnects for operably coupling the diestack to a logic die or a SoC die. Of course, semiconductor dice withina stack may have differing orientations, as desired.

As depicted in FIG. 2A, a base wafer, such as a silicon wafer 100′,having no integrated circuitry thereon has alignment marks A appliedthereto to facilitate die placement thereon at die stack locations DS.

In FIG. 2B, source wafers 200 having integrated circuitry 212, forexample, memory circuitry for a plurality of dice, fabricated on activesurface 214 thereof and conductive through via precursor structures 218′extending therethrough are probed and tested at wafer level tocharacterize those suitable for use as KGD.

As shown in FIG. 2C, some of source wafers 200 have a passivationmaterial 215 applied thereto, such as a polyimide, polybenzoxazole(PBO), or bismaleimide triazine (BT) resin, or silicon nitride, andthermally and electrically conductive elements 216 comprising metalpillars, such as copper pillars, may be formed in a pattern of aperturestherethrough in contact with conductive through via precursor structures218′. Thermally and electrically conductive elements 216 may alsocomprise solder balls, which may be formed as described above byreflowing solder paste segments or partially reflowing preformed solderballs on under bump metallization (UBM), for example nickel, exposedthrough apertures in a silicon nitride passivation layer. All of thesource wafers 200, including both those with thermally and electricallyconductive elements 216 and those without, may be mounted on temporarycarriers TC (see FIG. 2D) as known in the art and thinned as indicatedat broken line T (FIG. 2C) to, for example, a thickness of about 50 μmto expose the ends of conductive through via precursor structures 218′on a back side 220 of each wafer 200, forming conductive through vias218. An abrasive process, such as back grinding, followed by a silicondry etch process, may be used to thin wafers 200.

FIG. 2D depicts coating of the back side 220 of a thinned source wafer200 with a polymer passivation material 221 such as a polyimide, PBO orBT resin, or silicon nitride or a silicon oxide, and solderableinterconnects in the form of landing pads 222, for example, of nickel onthe ends of conductive through vias 218 comprising copper, areelectroplated.

In FIG. 2E, a thinned source wafer 200 is mounted to a film frame F, andtemporary carrier TC is removed. Wafer 200 is then singulated intoindividual dice 210.

In FIG. 2F, individual dice 210 a of a configuration without thermallyand electrically conductive elements 216 thereon are mounted to a basewafer 100′ devoid of integrated circuitry in laterally spacedrelationship at die stack locations (FIG. 2A) leaving streets Stherebetween as also shown in FIG. 4 with respect to the first describedembodiment using alignment marks (not shown) using a die attach film(DAF) D of, for example, about 10 μm to about 20 μm thickness, which isthen cured to affix dice 210 a to base wafer 100′, or a flowabledielectric material.

As depicted in FIG. 2G, a non-conductive epoxy paste 232 is dispensed ateach die stack site over a die 210 a and another die 210 b havingthermally and electrically conductive elements 216 extending from asurface thereof, is disposed thereover with elements 216 aligned withlanding pads 222. The non-conductive epoxy paste 232, which includes asolder flux, is displaced from between landing pads 222 and elements 216by compression of die 210 b against die 210 a. As an alternative, ano-flow epoxy underfill 232′ may be preapplied to the back side of die210 a.

As further depicted in FIG. 2G at the left-hand side in broken lines,rather than using a specially configured die 210 a without thermally andelectrically conductive elements 216, recesses RE to accommodate suchelements 216 may be dry etched, such as by reactive ion etching, intobase wafer 100′ using a conventional masking, patterning and etchingtechnique. Die 210 with elements 216 extending therefrom may then beadhered to wafer 100′ using a flowable dielectric material. FIG. 5depicts a portion of the base wafer 100′ with recesses RE as viewed fromabove within a die and elements 216 received therein, the footprint of asemiconductor die 210 bearing elements 216 also being shown forreference. In such an arrangement, semiconductor dice of the pluralityof laterally spaced semiconductor dice 210 are placed onto the basewafer with conductive elements 216 thereof at least partially receivedin a corresponding plurality of recesses RE in the base wafer 100′.

As additionally depicted in FIG. 2G, at the right-hand side thereof andas shown in broken lines, a recess RD, which may also be characterizedas a cavity to accommodate some or substantially all of the depth of adie 210 a may, again, be etched into base wafer 100′ to minimize theheight of the die stack being fabricated. FIG. 6 depicts a portion ofthe base wafer 100′ with recesses RE as viewed from above and thefootprint of a semiconductor die 210 a at least partially receivedtherein. In such an arrangement, semiconductor dice 210 a of theplurality of semiconductor dice may be at least partially placed intolaterally spaced recesses in the base wafer 100′.

Of course, a die recess RD may be formed, followed by recesses RE in thebottom thereof, as desired.

As also shown in FIG. 2G, the die stacking sequence is repeated for aplurality of dice 210 c, 210 d having conductive elements extending fromsurfaces thereof at each die site over previously stacked dice 210 a,210 b to faun a die stack 230. As before, a non-conductive paste 232 maybe employed, and the non-conductive paste 232 cured after the die stack230 is completed, or a preapplied no-flow epoxy underfill 232′ may beemployed.

As an alternative to the use of a non-conductive paste or a pre-appliedepoxy underfill, a flux may be applied to landing pads 222 of each die210 when solder balls are employed as elements 216, the solder ballsreflowed to bond to landing pads 222, then cooled and a capillaryunderfill disposed between the dice 210 of each die stack 230.

Securing the semiconductor dice 210 b, 210 c and 210 d to one anotherand to a semiconductor die 210 a of the plurality of laterally spacedsemiconductor dice may be effected after a die stack 230 is completed orone level at a time, using one of solder reflow, thermocompressionbonding and ultrasonic bonding, depending upon the material used forthermally and electrically conductive elements.

In FIG. 2H, the die stacks 230 are overmolded on base wafer 100′ using,for example, film assisted molding or compression molding of anelectrically insulative material, to provide a covering encapsulationstructure 234 around and between die stacks 230, resulting inencapsulated die stacks 236.

As shown in FIG. 2I, a redistribution layer comprising conductive traces240 and probe pads 242, for example, of copper, is formed byelectroplating followed by masking, patterning and etching, over theback side 220 of each die 210 d farthest from base wafer 100′. Backsides 220 of dice 210 d are then repassivated 244 as shown in FIG. 2J,and patterned over the ends of conductive through vias 218. Back sidethermally and electrically external connection conductive elements 246electroplated thereon as shown in FIG. 2K.

In FIG. 2K, base wafer 100′ with encapsulated die stacks 236, is thinnedusing, for example, back grinding, to a thickness of, for example, about50 μm to about 150 μm. A citric acid dip may then be employed to cleanthe copper probe pads 242 in preparation for conducting a test of eachdie stack, after which the locations of good die stack locations asdetermined by a test may be laser marked on base wafer 100′.

As shown in FIG. 2L, wafer 100′ repopulated with encapsulated die stacks236 may then be placed on a film frame F and singulated through theencapsulant structure 234 and through the body of wafer 100′ intostacked die packages 250, each comprising semiconductor dice 210 a-210 dand a base wafer segment 238. As with a previous embodiment, base wafersegment 238 provides a heat sink for enhanced thermal performance of thestacked die package 250.

Thus, before singulating through the encapsulant material and throughthe base wafer between stacks of semiconductor dice, contacts toconductive through vias of semiconductor dice farthest from the basewafer are left at least partially free of encapsulant material, andredistribution circuitry including pads for testing in communicationwith conductive through vias is formed over a back side of eachsemiconductor die farthest from the base wafer in a stack, passivationis applied over a back side of each semiconductor die farthest from thebase wafer in a stack and the pads and contacts to the conductivethrough vias thereof are left exposed, and external connectionconductive elements over and connected to contacts to the conductivethrough vias are formed.

Following singulation, stacked die packages 250 may be removed from thefilm frame by a pick-and-place apparatus and disposed in pockets 260 ina tape 262 as shown in FIG. 2M for use in a tape and reel device of acustomer, and shipped to the customer. Of course, the stacked diepackages 140 of the first embodiment may be packaged for shipping in asimilar manner.

A completed, inverted stacked die package 250 is depicted in FIG. 2N. Anend view of stacked die package 250 showing traces 240, probe pads 242,passivation 244 and external connection conductive elements 246 isdepicted in FIG. 2O.

In the foregoing embodiment, active surfaces of the stackedsemiconductor dice are, due to their orientation facing the base wafer,well protected during processing. The probe pads enable probe testing ofthe stacked dice at the wafer level in such an orientation.

A resulting semiconductor die assembly of the disclosure may comprise awafer segment having no integrated circuitry thereon, a stack ofsemiconductor dice of lesser lateral dimensions that the wafer segmentsecured to a surface thereof in thermally conductive communicationtherewith, the semiconductor dice mutually operably coupled byconductive elements therebetween in conductive contact with conductivethrough vias of the semiconductor dice, a non-conductive materialbetween the semiconductor dice of the stack, and an encapsulant materialextending peripherally about the dice of the stack and in contact withthe surface of the wafer segment.

The semiconductor die assembly may further comprise, on a back side ofthe semiconductor die of the stack farthest from the wafer segment, atleast partially exposed contacts to conductive through vias,redistribution circuitry including pads for testing of the stack ofsemiconductor dice operably coupled to conductive through vias, externalconnection conductive elements extending from the semiconductor die overand operably coupled to the at least partially exposed contacts to theconductive through vias, and passivation leaving the pads and externalconnection conductive elements exposed.

The wafer segment may further comprise a cavity extending into thesurface and a semiconductor die of the stack adjacent to the wafersegment is at least partially received in the cavity.

The surface of the wafer segment may comprise a plurality of recessesand conductive elements extending from the active surface of asemiconductor die of the stack adjacent the wafer segment may be atleast partially disposed in the plurality of recesses.

Referring now to FIGS. 3A through 3C, FIG. 3A depicts a schematic of astacked die package 140, 250 according to an embodiment of thedisclosure and as previously described herein, respectively, with regardto FIGS. 1G and 2M. In FIG. 3B, a logic die or SoC die 300 isschematically depicted mounted and electrically connected by conductiveelements 302 to traces (not shown) of a carrier substrate, such as aball grid array (BGA) substrate 304, having conductive elements 306, forexample, solder balls, extending therefrom for connection tohigher-level packaging. FIG. 3C depicts a stacked die package 140, 250mounted and electrically connected to logic die or SoC die 300 andovermolded with a dielectric encapsulant material 308. As depicted inFIG. 3C, stacked die package 140, 250 may be of greater lateral extentthan logic die or SoC die 300, with encapsulant material 308 extendingover and around stacked die package 140, 250, filling a peripheralrecess between stacked die package 140, 250 and carrier substrate 304around logic die or SoC die 300 and in contact with BGA substrate 304.

A semiconductor device as described above comprises a carrier substratecomprising external connections on a surface thereof, one of a logic dieand a system on a chip die mounted on an opposing surface of the carriersubstrate and operably coupled to the external connections thereof, andan assembly. The assembly comprises a wafer segment devoid of integratedcircuitry, a stack of semiconductor dice on a surface of the wafersegment having conductive through vias thereof connected with conductiveelements extending therebetween and operably coupled to the one of alogic die and a system on a chip die, a non-conductive material betweenthe semiconductor dice of the stack, and at least one encapsulantmaterial extending over the wafer segment and peripherally about thewafer segment, the stack of semiconductor dice and the one of the logicdie and the system on a chip die and in contact with the carriersubstrate.

CONCLUSION

In one embodiment, a method of forming a semiconductor die assemblycomprises securing a plurality of laterally spaced semiconductor dice toa base wafer, disposing at least two semiconductor dice over eachsemiconductor die of the plurality to foam a stack and connectingconductive through vias of the semiconductor dice in a stack withconductive elements extending therebetween, providing a dielectricmaterial between the semiconductor dice in a stack, substantiallysimultaneously encapsulating at least a periphery of each of the stacksof semiconductor dice on the base wafer with an encapsulant materialbetween and around the stacks of semiconductor dice, and singulating thestacks of semiconductor dice and the base wafer through the encapsulantmaterial between the stacks of semiconductor dice.

Another embodiment comprises a method of forming a semiconductor dieassembly, comprising securing a plurality of laterally spacedsemiconductor dice having conductive through vias to a base wafer havingthermally conductive elements protruding therefrom in alignment with theconductive through vias, stacking a plurality of semiconductor die overeach semiconductor die of the plurality of laterally spacedsemiconductor dice and connecting conductive through vias of stackedsemiconductor dice with conductive elements extending therebetween,introducing a dielectric material between the semiconductor dice,substantially simultaneously encapsulating at least a periphery of thesemiconductor dice on the base wafer with an encapsulant materialbetween and around the semiconductor dice, and severing through theencapsulant material and through the base wafer between stacks ofsemiconductor dice.

Yet another embodiment comprises a semiconductor die assembly,comprising a wafer segment having no integrated circuitry thereon, astack of semiconductor dice of lesser lateral dimensions that the wafersegment secured to a surface thereof in thermally conductivecommunication therewith, the semiconductor dice mutually operablycoupled by conductive elements therebetween in conductive contact withconductive through vias of the semiconductor dice, a non-conductivematerial between the semiconductor dice of the stack, and an encapsulantmaterial extending peripherally about the dice of the stack and incontact with the surface of the wafer segment.

A further embodiment comprises a semiconductor device, comprising acarrier substrate comprising external connections on a surface thereof,one of a logic die and a system on a chip die mounted on an opposingsurface of the carrier substrate and operably coupled to the externalconnections thereof, and an assembly comprising a wafer segment devoidof integrated circuitry, a stack of semiconductor dice on a surface ofthe wafer segment having conductive through vias thereof connected withconductive elements extending therebetween and operably coupled to theone of a logic die and a system on a chip die, a non-conductive materialbetween the semiconductor dice of the stack, and at least oneencapsulant material extending over the wafer segment and peripherallyabout the wafer segment, the stack of semiconductor dice and the one ofthe logic die and the system on a chip die and in contact with thecarrier substrate.

While the disclosure is susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, the invention is not intended to be limited to the particularforms disclosed. Rather, the invention encompasses all modifications,equivalents, and alternatives falling within the scope of the inventionas defined by the following appended claims and their legal equivalents.

What is claimed is:
 1. A method of forming a semiconductor die assembly,comprising: forming a dielectric material over a surface of a basewafer; forming a plurality of thermally conductive elements on thedielectric material in electrical isolation from the base wafer; placingconductive through vias of a plurality of laterally spaced semiconductordice in contact with the thermally conductive elements; disposing atleast two semiconductor dice over each semiconductor die of theplurality to form a stack and connecting conductive through vias of thesemiconductor dice in a stack with conductive elements extendingtherebetween; providing a dielectric material between the semiconductordice in a stack; substantially simultaneously encapsulating at least aperiphery of each of the stacks of semiconductor dice on the base waferwith an encapsulant material between and around the stacks ofsemiconductor dice; and singulating the stacks of semiconductor dice andthe base wafer through the encapsulant material and the base waferbetween the stacks of semiconductor dice.
 2. The method of claim 1,further comprising connecting the at least two semiconductor dice to oneanother and to a semiconductor die of the plurality of laterally spacedsemiconductor dice using one of solder reflow, thermocompression bondingand ultrasonic bonding.
 3. The method of claim 1, wherein stacking atleast two semiconductor dice over each semiconductor die of theplurality of laterally spaced semiconductor dice secured to the basewafer comprises stacking at least two semiconductor dice havingconductive elements extending from surfaces thereof.
 4. The method ofclaim 1, further comprising placing semiconductor dice of the pluralityof laterally spaced semiconductor dice at least partially into laterallyspaced recesses in the base wafer.
 5. The method of claim 1, furthercomprising placing semiconductor dice of the plurality of laterallyspaced semiconductor dice onto the base wafer with conductive elementsthereof at least partially received in a corresponding plurality ofrecesses in the base wafer.
 6. The method of claim 1, further comprisingorienting each semiconductor die in a stack with active surfaces thereoffacing in a common direction.
 7. The method of claim 1, furthercomprising orienting each semiconductor die in a stack with activesurfaces facing the base wafer.
 8. The method of claim 1, furthercomprising, before singulating the stacks of semiconductor dice throughthe encapsulant material and through the base wafer: thinning the basewafer; conducting a test of each die stack; and marking good die stacklocations as determined by a test.
 9. The method of claim 1, whereinsecuring a plurality of laterally spaced semiconductor dice to a basewafer comprises securing a plurality of semiconductor dice to a basewafer having no integrated circuitry thereon.
 10. A method of forming asemiconductor die assembly, comprising: securing a plurality oflaterally spaced semiconductor dice to a base wafer; disposing at leasttwo semiconductor dice over each semiconductor die of the plurality toform a stack and connecting conductive through vias of the semiconductordice in a stack with conductive elements extending therebetween;providing a dielectric material between the semiconductor dice in astack; substantially simultaneously encapsulating at least a peripheryof each of the stacks of semiconductor dice on the base wafer with anencapsulant material between and around the stacks of semiconductordice; leaving contacts to conductive through vias of semiconductor dicefarthest from the base wafer at least partially free of encapsulantmaterial; forming redistribution circuitry including pads for testing incommunication with conductive through vias over a back side of eachsemiconductor die farthest from the base wafer in a stack; applyingpassivation over a back side of each semiconductor die farthest from thebase wafer in a stack and leaving the pads and contacts to theconductive through vias thereof exposed; forming external connectionconductive elements over and connected to contacts to the conductivethrough vias; and singulating the stacks of semiconductor dice and thebase wafer through the encapsulant material and the base wafer betweenthe stacks of semiconductor dice.
 11. A method of forming asemiconductor die assembly, comprising: securing a plurality oflaterally spaced semiconductor dice having conductive through vias to abase wafer having thermally conductive elements protruding therefrom inalignment with the conductive through vias; stacking a plurality ofsemiconductor die over each semiconductor die of the plurality oflaterally spaced semiconductor dice and connecting conductive throughvias of stacked semiconductor dice with conductive elements extendingtherebetween; introducing a dielectric material between thesemiconductor dice; substantially simultaneously encapsulating at leasta periphery of the semiconductor dice on the base wafer with anencapsulant material between and around the semiconductor dice; thinningthe base wafer; conducting a test of each die stack; marking good diestack locations as determined by a test; and severing through theencapsulant material and through the base wafer between stacks ofsemiconductor dice.
 12. The method of claim 11, wherein stacking aplurality of semiconductor dice over each semiconductor die of theplurality of laterally spaced semiconductor dice secured to the basewafer comprises stacking at least two semiconductor dice havingconductive elements extending from surfaces thereof.
 13. The method ofclaim 11, further comprising connecting the plurality of semiconductordice to one another and to a semiconductor die of the plurality oflaterally spaced semiconductor dice using one of solder reflow,thermocompression bonding and ultrasonic bonding.
 14. The method ofclaim 11, further comprising orienting each semiconductor die in a stackwith active surfaces thereof facing in a common direction.
 15. Themethod of claim 11, further comprising orienting each semiconductor diein a stack with active surfaces facing away from the base wafer.
 16. Themethod of claim 11, wherein securing a plurality of laterally spacedsemiconductor dice to a base wafer comprises securing a plurality ofsemiconductor dice to a base wafer devoid of integrated circuitry.
 17. Amethod of forming a semiconductor die assembly, comprising: forming adielectric material over a surface of a base wafer; placing conductivethrough vias of a plurality of laterally spaced semiconductor dice incontact with the dielectric material to electrically isolate theconductive through vias from the base wafer; disposing at least twosemiconductor dice over each semiconductor die of the plurality to forma stack and connecting conductive through vias of the semiconductor dicein a stack with conductive elements extending therebetween; providing adielectric material between the semiconductor dice in a stack;substantially simultaneously encapsulating at least a periphery of eachof the stacks of semiconductor dice on the base wafer with anencapsulant material between and around the stacks of semiconductordice; and singulating the stacks of semiconductor dice and the basewafer through the encapsulant material between the stacks ofsemiconductor dice.
 18. The method of claim 17, wherein forming adielectric material over a surface of a base wafer comprises forming oneof a die attach film and a flowable dielectric material, and furthercomprising securing the plurality of laterally spaced semiconductor diceto the base wafer with one of the die attach film and the flowabledielectric material.